my hard drive filled up suddenly virus, worm?

I noticed my hard drive filling up, and now i am almost completely out of space. Virus scans have found nothing (I have windows defender, and I downloaded Sophos for an additional scan) but I know something has infected my computer. I keep getting messages telling me my backup has failed (not enough space on my cloud), but that is because something is taking up my memory, and fast! I'm afraid it may crash.

The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Purch hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.